Can't get power button symbol right. Need help cutting letter 'O' and filling gaps
Here is how you can create a power button:


Add a circle.
Enter edit mode.
Selected it(A) and extrude + scale it inwards.
Delete(X->Faces) some of the at the top of the circle as such:

Add a plane into the scene.
scale the plane so that it takes the shape of the line:

Select All(A), and extrude it upwards until your power button is as thick as you want it.
To add rounded edges: select the line, as well as the faces on the inside of the cut. also select the rings(Shift-Alt) that make up the edges of the '0'.
With all those vertices selected hit Ctrl-B. Use the scroll wheel to control the amount of cuts(I'd recommend 4).
Select all and hit W->Shade Smooth.
Rotate it on the Y axis to 90 degrees (RY90) .


Done!